Field of the Invention
The invention relates to a touch sensing technique, and particularly relates to an optical touch sensing device having a plurality of optical sensing modules and a sensing method thereof.
Description of Related Art
Electronic devices or display screens having a touch function have gradually become a development trend of today's technology. However, limited by manufacturing cost and a touch effect, capacitive or resistive touch screens are only adapted to small and middle-size devices such as mobile phones, tablet personal computers (PCs), notebooks, and all-in-one (AIO) computers, and are not suitable for being applied to large-size devices due to reasons of cost, reliability, etc. Along with development of photosensitive elements, large-size screens (for example, electronic whiteboards or advertising billboards) generally adopt an optical touch technique to implement a touch function, and a reason thereof is that the optical touch technique not only results in a low manufacturing cost, a touch accuracy thereof is also improved along with development of technology, and along with advance of identification algorithm, multi-touch operations can be effectively detected. An application principle of the optical touch technique is to detect a position of a finger by detecting a light shielded or reflected by a touch object, and convert such position into a position of the touch object on the screen to implement the touch function.
The present optical touch technique generally adopts a touch device composed of two optical sensing modules (for example, optical cameras) and a processing unit (for example, a central processing unit (CPU), a field programmable gate array (FPGA), etc.) applied therein to detect the touch object. However, when the number of the touch objects is greater than two, it is complicated for the processing unit to identify and calculate positions of touch points, and an error or an interference is liable to be occurred, for example, the so-called “ghost points problem”. For example, when two touch objects are simultaneously located in a touch area, four intersections are generated under a function that the two optical cameras cross-capture images, in which two intersections are real touch points and the other two intersections are ghost points without the touch object. Now, the processing unit further determines and selects the touch points according to various physical phenomenon or variations (for example, the previously detected touch points).
A current solution is to additionally add the touch devices at different locations of the touch area to assist determining the touch points and filtering the ghost points. However, when the touch devices are increased, the method for determining the touch points becomes more complicated, and a required computation amount is also increased. On the other hand, the touch device composed of more than two optical sensing modules also has areas with less sensing accuracy, for example, when the position of the touch object is very close to a connection line between the two optical sensing modules, the intersection sensed by the touch device is inaccurate. Alternatively, limited by an image resolution of the optical sensing modules, the touch device cannot accurately identify or determine the real touch points and ghost points located beyond a certain large distance or within a certain angle range, which may lead to a wrong judgement for the real touch points.